Theoretical Study Of Nitrogen,Hydrogen And Ammonia Adsorption On The Pyrite FeS₂?100?Surfaces

The continuous increase of world population and rapid development of industry have expanded the demand for ammonia.Although there is a large amount of nitrogen in the air,it has to be transformed into ammonia through nitrogen fixation process?the reduction of atmospheric dinitrogen to ammonia?,since dinitrogen is chemically inert and could not be used directly by living organisms.The traditional ammonia synthesis?Haber-Bosch process?proceeds under harsh conditions of high temperature??500 ??and high pressure?-20 MPa?in the presence of catalyst,and a large amount of energy has been consumed.In recent years,researches have found that pyrite FeS₂ may play an important role in the origin of life by the way of nitrogen fixation.In this thesis,the adsorption of nitrogen,hydrogen and ammonia on pyrite FeS₂?100?surfaces has been studied using the first-principles calculation method based on density functional theory?DFT?.The interaction of nitrogen,hydrogen and ammonia with pyrite FeS₂?100?surface has been discussed.The main contents of this thesis are as follows:?1?Adsorption of N atoms and N₂ molecules on pyrite FeS₂?100?surfaces.S-terminated?1×1?and?2×2?FeS₂?100?surfaces were constructed.The most stable adsorption sites for both N atoms and N₂ molecules are the near-top site above Fe atom.Adsorption stability gradually decreases with the increase of the N atom coverage.Compared to N₂ molecule,the adsorption of N atom on the surface of FeS₂?100?is more stable.?2?Adsorption of H atoms and H₂ molecules on pyrite FeS₂?100?surfaces.For H atoms,the most stable adsorption site is the near-top site above Fe atom.Adsorption stability gradually decreases with the increase of the H atom coverage.However,for H₂ molecule,although it composed by two hydrogen atoms,it is quite difficult to adsorb on pyrite?100?surfaces.?3?Adsorption of NH,NH₂ and NH₃ on pyrite FeS₂?100?surfaces.Simulations on the adsorption of these species on S-terminated and Fe-terminated?100?surfaces of pyrite FeS₂ has been carried out contrastively.For the adsorption on S-terminated surface,NH adsorbs on the top of S-Fe bridge site,while NH₂ adsorbs at the near-top site above S atom.For the adsorption on Fe-terminated surface,the adsorption sites for both NH and NH₂ are the near-top site above Fe atom.The adsorption sites for NH₃ adsorbing on both S-terminated and Fe-terminated surfaces are near-top sites above Fe atom.In terms of adsorption stability,the stability of NH on the FeS₂?100?surface is stronger than that of NH₂,while the adsorption stability of NH₃ is the weakest.The results of these theoretical calculations were compared with experimental conclusions.In addition,the influence of NH₃ coverage,density of states and the distribution of electrons have also been studied.